These studies will examine the adult and developing neuronal structure of the visual cortex (area 17) of the macaque monkey in Golgi preparations of foetal and postnatal material. Correlative studies using the electron microscope will relate the synaptology of individual elements to the overall structural relationships seen by the light microscope. Orthograde and retrograde axonal transport techniques will be used to identify afferent and efferent relations of area 17. The effects of visual deprivation on the structural development of area 17 will be assessed. A second area of study will use the rat to determine factors governing development, distribution, and degree of plasticity of different types of optic nerve fibers. A combination of light and electron microscopic approaches will be used. This work should provide a morphological background to physiological studies on mature, developing and visually deprived primate cortex. The developmental approaches should give a baseline for understanding the nature and causes of defects arising during early formation of neuronal connections.